1. Field of the Invention
The present invention relates to a plasma display apparatus and, more particularly, to a method and a circuit for driving a plasma display panel (PDP) in which an input image data is processed with a minimum block unit so as to realize 256 gray levels.
2. Discussion of the Related Art
Conventionally, a PDP is discharged by adjusting a voltage applied to between vertical and horizontal electrodes of a cell, and an amount of discharged light is adjustable by varying a discharging time within each cell.
The entire screen of a PDP is obtained operating in matrix by applying a light pulse for inputting an image signal into vertical and horizontal electrode of each cell, a scan pulse for scanning, a sustain pulse for maintaining discharge, and an erase pulse for stopping the discharge of the discharged cell.
Gradation of brightness (gray levels) required for image display is obtained by varying a discharging time of each cell within a period required for displaying an entire image (1/30 second as for NTSC TV). A luminance of a screen is determined by a brightness which is made when each cell is operated at its maximum. A driving circuit must be designed to maintain a discharging time of a cell as long as possible within a time allowed for constituting a screen, so as to increase its luminance.
FIG. 1 is a block diagram of a general PDP driving circuit illustrated in U.S. Pat. No. 5,446,344. The PDP driving circuit includes a glass substrate where scan electrodes and common electrodes are formed and a panel 1 formed by vacuum connection of a rear glass substrate where an addressing electrode is formed, an addressing electrode driver 4 for applying a digital image data to the addressing electrode formed on the rear glass substrate, a scan driver 3 for applying a scan pulse for determining whether the panel 1 is driven or not, a common electrode driver 5 for driving the common electrode of the panel 1, and a controller 2 for providing signals and data necessary for driving the drivers 3, 4, and 5.
The controller 2 in such a PDP having the aforementioned structure is provided with various signals, such as clock signals, RGB data, vertical and horizontal synchronizing signals Vsync and Hsync. Subsequently, the controller 2 applies scan data and control data into the scan driver 3 and address data and address clock signals into the addressing electrode driver 4. The scan electrode and the common electrode are driven according to the signals applied into each of the drivers, and then data supplied to the addressing electrodes can be displayable on the panel 1.
A sub-field method and a sub-frame method, which are methods for driving a PDP, will be described.
In sub-field method, a frame is divided into X number of sub-fields, thus realizing 2.sup.X number of gray levels. Since each sub-field corresponds to a luminance value in proportion to a luminance relative ratio of 1:2:4:8:16:32:64:128, combination of several sub-fields serves to display a pixel corresponding to a gradation data (0.about.(2.sup.x -1). For example, as shown in FIG. 2, after a frame is divided into 8 sub-fields SF.sub.1 -SF.sub.8, each of the sub-fields SF.sub.1 -SF.sub.8 is made to correspond to a luminance value in proportion to a ratio of 1:2:4:8:16:32:64:128 so that a combination of several sub-fields can serve to display a pixel corresponding to d gradation data 0.about.255 (usually displayed as 8 bit D.sub.7.about.D.sub.0). As a result, 256 gray levels can be realized.
That is to say, D.sub.0 bit gradation data, an LSB among gradation data of each cell, is provided for each cell on driving a first sub-field SF.sub.1, and D.sub.1, D.sub.2, D.sub.3, D.sub.4, D.sub.5, D.sub.6, D.sub.7, bit gradation data are provided for corresponding cells on driving second, third, fourth, fifth, sixth, seventh, and eighth sub-fields SF.sub.2 -SF.sub.8, respectively. Accordingly, a specific cell is luminated and discharge of the specific cell is maintained for a predetermined time for each of the sub-fields SF.sub.1 -SF.sub.8, thus displaying a pixel.
However, in the sub-field driving method, since a gradation data of an identical bit corresponding to each sub-field is provided for each cell, it is easy to obtain a gradation data, but since a entire cell corresponding to each sub-field can be erasable and dischargeable, a picture flicker is caused.
In order to solve the aforementioned problem, a sub-frame driving method has been proposed. In this method, a frame is divided into X number of sub-frames to obtain 2.sup.X number of gray levels. Each of the sub-frames includes lines of as many as a number in proportion to a luminance relative ratio 1:2:4:8:16: . . . . For example, as shown in FIG. 3, each of 8 sub-frames sf.sub.1 -sf.sub.8, which a frame has been divided into, has lines of as many as a corresponding number in proportion to the ratio of 1:2:4:8:16:32:64:128. Every other 8 lines are being scanned repeatedly at a time until the total lines are scanned 8 times such that pixels corresponding to gradation data 0-256 can be displayed, thus realizing 256 gray levels.
That is to say, if a frame is divided into 8 sub-frames sf.sub.1 -sf.sup.8, when a number of total lines is 255, first, second, third, fourth, fifth, sixth, seventh, and eighth sub-frames sf.sub.1 -sf.sub.8, have a 255th line (total one line), 254th line to 253rd line (total 2 lines), 252nd line to 249th line (total 4 lines), 248th line to 241st line (total 8 lines), 240th line to 225 line (total 16 lines), 224th line to 193 line (total 32 lines), 192nd line to 129th line (total 64 lines), and 128th line to 1st line (total 128 lines), respectively.
The first lines (the 255th line, 253rd line, 249th line, 241st line, 225th line, 193rd line, 129th line, and 1st line) corresponding to the eight sub-frames sf.sub.1 -sf.sub.8, respectively, are sequentially scanned at a time with gradation data of bit corresponding to the above mentioned lines provided. Then, discharge erase of entire lines is carried out.
Next, another eight lines following the scanned eight lines are sequentially scanned at a time as shown in the following table and a gradation data of bit corresponding to each line is provided. Thereafter, discharge erase is repeatedly carried out over the entire lines, thereby realizing 256 gray levels.
order sf.sub.1 sf.sub.2 sf.sub.3 sf.sub.4 sf.sub.5 sf.sub.6 sf.sub.7 sf.sub.8 1 255 253 249 241 225 193 129 1 2 1 254 250 242 226 194 130 2 3 2 255 251 243 227 195 131 3 4 3 1 252 244 228 196 132 4 5 4 2 253 245 229 197 133 5 6 5 3 254 246 230 198 134 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 249 247 243 235 219 187 123 250 251 250 248 244 236 220 188 124 251 252 251 249 245 237 221 189 125 252 253 252 250 246 238 222 190 126 253 254 253 251 247 239 223 191 127 254 255 254 252 248 240 224 192 128 255
For example, the first lines of all sub-frames sf.sub.8, sf.sub.1, sf.sub.2, sf.sub.3, sf.sub.4, sf.sub.5, sf.sub.6, and sf.sub.7, are scanned at the 1st, 2nd, 4th, 8th, 16th, 32nd, 64th, and 128th sequences, respectively, thereby providing gradation data. A gradation data provided at the first sequence is sustained one until another gradation data is provided at the second sequence. In the same way, the gradation data provided at the 2nd sequence is sustained twice until another gradation data is provided at the fourth sequence. Accordingly, gradation data provided at the 1st, 2nd, 4th, 8th, 16th, 32nd, 64th, and 128th sequences are sustained once, twice, four times, eight times, sixteen times, thirty two times, sixty four times, one hundred twenty eight times, respectively. That is to say, at the first sequence, a gradation data of least significant bit (LSB) D.sub.0 is provided for the first line. In the same way, at the 2nd, 4th, 8th, 16th, 32nd, 64th, and 128th sequences, gradation data of bits D.sub.1, D.sub.2, D.sub.3, D.sub.4, D.sub.5, D.sub.6, D.sub.7 should be provided for the first lines.
Besides the first lines, a gradation data of a corresponding bit should be provided for every line according to a corresponding sustaining time. For example, 1st, 254th, 250th, 242nd,, 226th, 194th, 130th, and 2nd lines should be provided with gradation data of D.sub.1, D.sub.2, D.sub.3, D.sub.4, D.sub.5, D.sub.6, D.sub.7, D.sub.0 bits, respectively.
It is very complex and takes too much time to realize gradation data by utilizing the previously described sub-frame driving method. Accordingly, much development and research has been directed to real time processing of image data